Vacuum-pressure swing absorption concentrator

ABSTRACT

A vacuum-pressure swing absorption concentrator includes a motor driven compressor having pressure and vacuum heads that are connected to a pressure reservoir and a vacuum reservoir respectively. The pressure and vacuum reservoirs are selectively and alternately interconnected in sequence through a main valve to a pair of nitrogen filtering sieve beds. A controller operates the valve to alternately and cyclically interconnect the sieve beds to the pressure and vacuum reservoirs respectively. During each cycle, a respective bed is pressurized and enriched oxygen is produced and delivered to a tank for use by a patient. At the same time, the other bed is evacuated through the vacuum reservoir. A crossover valve delivers oxygen from a pressurized bed to an evacuated bed to facilitate purging of impurities previously collected in the evacuated bed.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/589,159 filed Oct. 19, 2009, now U.S. Pat. No. 8,236,095, entitled“Vacuum-Pressure Swing Absorption Concentrator,” which claims thebenefit of U.S. Provisional Patent Application Ser. No. 61/196,441 filedOct. 17, 2008, the disclosures of which are herein incorporated byreference.

FIELD OF THE INVENTION

This invention relates to an oxygen concentrator that produces enrichedoxygen for medical purposes utilizing vacuum-pressure swing absorption.More particularly, the concentrator exhibits a highly efficientoperation by incorporating pressure and vacuum reservoirs between thecompressor and sieve beds.

BACKGROUND OF THE INVENTION

Oxygen concentrators are commonly used to provide enriched oxygen topatients having respiratory problems. Conventional concentratorstypically operate on the principles of pressure swing absorption, vacuumswing absorption or vacuum-pressure swing absorption. According to thesetechniques, air is delivered under pressure to a sieve bed whereinnitrogen and other impurities are absorbed by a filter medium such aszeolite. The trapped air impurities are then purged and vented underreduced pressure or vacuum conditions. In some devices, pressurized airis delivered sequentially to two or more beds in an attempt to improvethe efficiency of the system.

Despite advancements in medical concentrator technology, known productsare still far from optimally efficient. The compressor used in most suchproducts must generate pressure and air flow that are sufficient toproduce an adequate volume of enriched oxygen for the patient. Thistypically requires the compressor and associated motor to draw asubstantial amount of electrical power. Portable concentrators utilizeconsumable batteries and the significant power demands of suchconcentrators tend to shorten battery life considerably. In addition,the body of a typical portable concentrator is apt to heat upexcessively when operating under the high pressure generated by thecompressor. This further reduces the operating efficiency of theapparatus. Moreover, if a compressor operating under high pressuredelivers a volume of air to the sieve beds faster than those beds canprocess the air, the motor driving the concentrator's compressor is aptto stall.

A further disadvantage exhibited by standard concentrators is that themotor is usually controlled to operate at a constant speed (RPM). Thistends to produce an inadequate volume of air over the concentratorcycle. If the operating speed is increased to increase air flow,excessive power is consumed and battery life is shortened.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anextremely efficient vacuum-pressure swing absorption concentrator thatproduces and delivers to the patient large and effective volumes ofenriched oxygen while requiring significantly less power than covered byconventional medical concentrators.

It is a further object of this invention to provide a medicalconcentrator that requires significantly less power to produce desiredvolumes of enriched oxygen so that battery life is significantlyprolonged.

It is a further object of this invention to provide an efficientvacuum-pressure swing absorption oxygen concentrator that isparticularly effective for portable use.

It is a further object of this invention to provide a vacuum-pressureswing absorption concentrator that produces much less heat thanconventional medical concentrators.

It is a further object of this invention to provide a vacuum-pressureswing absorption concentrator that reduces the amount of moistureintroduced into the sieve beds so that improved filter performance isachieved.

It is a further object of this invention to provide an oxygenconcentrator that improves sieve bed efficiency and concentratorportability by reducing the amount of filter medium and the size of thesieve beds needed to produce a desired volume of enriched oxygen.

It is a further object of this invention to provide an oxygenconcentrator that employs an amperage controlled motor in order toproduce increased volumes of enriched oxygen while requiring less powerthan concentrators using a speed controlled motor.

It is a further object of this invention to provide an oxygenconcentrator that employs main and crossover valves featuring equal airflow volumes during alternating flow cycles so that improved filteringefficiency and oxygen output are achieved.

It is a further object of this invention to provide an oxygenconcentrator that introduces enriched oxygen from the filter head beingpressurized to the other bed being evacuated before the end of eachpressurization cycle so that improved nitrogen filtration is achievedand less power is required.

This invention results from a realization that the operating efficiencyof a vacuum-pressure swing absorption concentrator is improvedsignificantly by installing both pressure and vacuum reservoirs betweenthe compressor and the sieve beds of the machine. This permits aneffective high volume of air flow to be generated through the filtermedium of the sieve beds. At the same time, reduced pressure and vacuumforces are exerted upon the compressor. As a result, the concentratoroperates much more efficiently and effectively, and requiressignificantly less power than is used by conventional machines.

This invention features a vacuum-pressure swing absorption concentratorfor delivering enriched oxygen to a medical patient. The concentratorincludes a motor driven compressor having intake and exhaust ports. Theair intake port is communicably connected to a pressure reservoir, whichaccommodates air pressurized by the compressor. The pressure reservoirincludes an outlet that is communicably connected to a main valve. Themain valve sequentially and alternately interconnects the pressurereservoir to communicate with a selected one of a pair of nitrogenfilters or sieve beds while communicably interconnecting the other bedwith a vacuum reservoir. The vacuum reservoir includes an outlet that iscommunicably interconnected to the exhaust port of the compressor. Themain valve is operated to deliver air from the pressure reservoir to aselected one of the sieve beds for filtering while simultaneouslydischarging or evacuating previously filtered impurities from the othersieve bed. Enriched oxygen, which has been filtered by the sieve beds,is then directed to a tank for ultimate delivery to a patient using theconcentrator.

In a preferred embodiment, the compressor includes a pair of heads forgenerating air under pressure and a vacuum respectively. A motor controlmechanism preferably featuring amperage control directs the motor tooperate at a relatively constant predetermined power. This achieves agreater air flow and more effective and efficient filtering than isobtained using concentrators wherein the speed (RPM) of the motor iscontrolled.

A controller may be utilized to operate the main valve so that the sievebeds are alternately and sequentially interconnected to the pressure andvacuum reservoirs. A crossover valve may be interconnected between thesieve beds. The controller, which may comprise a known type ofmicroprocessor, typically also directs the crossover valve to openshortly before each sieve bed is fully pressurized. Oxygen is therebydelivered to the other sieve bed (i.e. the bed being evacuated) and thishelps to purge filtered nitrogen and other impurities from that bed andfurther reduces system pressure. The crossover valve delivers a precise,equal volume of enriched oxygen alternately to each bed as that bed isunder vacuum. This improves overall oxygen production. If unequalvolumes are delivered (as in the prior art), one of the beds overworksand the efficiency and overall oxygen concentration generated by theconcentrator are significantly reduced. Check valves may be providedbetween the sieve beds and the enriched oxygen tank to direct the flowof enriched oxygen in one direction from the beds to the tank whilerestricting oxygen flow in the opposite direction.

Other objects, features and advantages will occur from the followingdescription of a preferred embodiment and the accompanying drawings, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the vacuum-pressure swing absorptionconcentrator of this invention; and

FIG. 2 is a graph that depicts the relative volumes of air produced bythe compressor using amperage motor control as disclosed by thisinvention versus standard RPM motor control.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

There is shown in FIG. 1 a vacuum-pressure swing oxygen concentrator 10for delivering enriched oxygen to a medical patient. The components ofconcentrator 10 are particularly effective for use in portable, batterypowered concentrators although the particular intended use of theconcentrator is not a limitation of this invention.

Concentrator 10 includes a compressor 12 having a pressure generatingsection or head 14 and a vacuum generating section or head 16. Thecompressor is operated by a DC motor 18 featuring an amperage controlcircuit 20, which may comprise a portion or all of DC motor control 21.Motor 18 is, in turn, energized by a battery power supply 19. Ascompressor 12 is operated in accordance with this invention, fresh airis drawn into the compressor through an air intake 22 and filtered in amanner described more fully below. After the filtration is performed andenriched oxygen is generated, filtered impurities are discharged by anexhaust port 24. Conventional compressors and associated components thatperform the foregoing functions will be known to persons skilled in theart.

A pressure reservoir 26 comprising an aluminum tank includes an inletthat is communicably connected to pressure head 14 of compressor 12. Anoutlet of pressure reservoir 26 is likewise communicably connected to aninlet of main control valve 28. The main valve also includes an outletthat is communicably connected to the inlet of a vacuum reservoir 30.The vacuum reservoir may again comprise a tank composed of aluminum orsimilar durable material. Vacuum head 16 of compressor 12 iscommunicably connected to an outlet of vacuum reservoir 30. Thecommunicable connections disclosed herein may be attached byconventional means such as tubes, pipes, hoses or other forms ofconduits.

Valve 28 is communicably joined to a first sieve bed 31 by a first sievebed connection 32. The main valve is likewise communicably joined tosecond sieve bed 34 by a second sieve bed connection 36. The sieve beds(also referred to as nitrogen filters) typically include a standardfiltering medium used in the medical oxygen concentrator industry.Various filter compositions (e.g. zeolite) may be employed within thescope of this invention. The size of each sieve bed may range fromapproximately the size of the pressure reservoir to a volume ten timesgreater than that of reservoir 26. Beds 30 and 34 are themselvesinterconnected by a crossover valve 38 that is selective opened, asdescribed below, to communicably join the beds.

Main valve 28 is constructed so that sieve beds 31 and 34 may beselectively, sequentially and alternately interconnected with pressurereservoir 26 and vacuum reservoir 30 respectively. Such alternating andselective communicable interconnection is accomplished by constructingmain valve 28 in accordance with a variety of valves available in theindustry and known to persons skilled in the art. Typically, valve 28exhibits a timed operation controlled by a controller 40, whichtypically comprises a microprocessor that is programmed to performtimed, sequential operation of the concentrator in the manner describedbelow. Controller 40 may also control the timed operation of crossovervalve 38. The valves may also be pressure cycle operated. Main valve 28is programmed to deliver a matched air flow alternately to each of beds31 and 34. Crossover valve 38 is likewise programmed to deliver amatched or equivalent flow of enriched oxygen between the sieve beds.

Air delivered to beds 31 and 34 is filtered therein to produce enrichedoxygen. This oxygen is then directed through oxygen outlet/output lines42 and 44 and check valves 46 and 48 respectively to product tank 50.From there, the product is directed through a flow meter 52 anddelivered to patient 54 as required. Various types of known conduits,tubes, pipes and fittings may be used to communicably connect the sievebeds to tank 50.

The volume of enriched oxygen in tank 50 is monitored by a pressuresensor 51, which is, in turn, connected to motor 18, through DC motorcontrol 21. When sensor 51 detects that the product tank is filled to aselected pressure, motor control 21 causes motor 18 to halt operation.As a result, the battery is not needlessly drained when the product tankis full. The motor operates more efficiently and battery life isprolonged. Alternating types of sensors/controls may be used toselectively stop the motor when the product tank approaches or reaches afull condition.

In operation, motor 18 employs a constant amperage controlled by circuit20 (as described more fully below). The motor thereby operatescompressor 12 to pump air sequentially to sieve beds 31 and 34. Inparticular, air is drawn through air intake 22 and pressurized bypressure head 14. Pressurized air is directed by arrow 60 into pressurereservoir 26. Controller 40 is programmed so that main valve 28initially delivers pressurized air from reservoir 26 throughcommunicable connection 32 to sieve bed 31. This air is then filtered bythe filtering medium in the sieve bed and delivered through valve 46 totank 50. At the same time, vacuum head 16 draws a vacuum upon sieve bed34 through vacuum reservoir 30, main valve 28 and communicableconnection 36.

At a predetermined time, controller 40 reverses the connection of sievebeds 31 and 34 to pressure and vacuum reservoirs 26 and 30 respectively.Specifically, main valve 28 communicably joins pressure reservoir 26 tosieve bed 34 through connection 36. At the same time, the main valvecommunicably joins sieve bed 31 to vacuum reservoir 30 throughconnection 32. A large volume of pressurized air from reservoir 26 isintroduced into bed 34. This air is filtered by the medium in bed 34 andthen delivered through line 44 and check valve 48 to enriched oxygentank 50. Meanwhile, nitrogen and other impurities remaining in sieve bed31 from the prior cycle are evacuated from sieve bed 31 through mainvalve 28 and into vacuum reservoir 30. The impurities are then drawn bypressure head 16 and discharged by exhaust port 24. Check valve 46prevents previously enriched oxygen from being drawn in reverse fromtank 50.

The concentrator continues to sequentially cycle in a timed, controlledmanner so that enriched oxygen is continuously produced and impuritiescontemporaneously removed in a cyclical, alternating manner from therespective sieve beds. Shortly before the end of each pressurizationcycle, controller 40 opens crossover valve 38 so that the sieve bedbeing pressurized delivers oxygen through the crossover valve to the bedundergoing evacuation. For example, shortly (i.e. approximately onesecond) before sieve bed 31 is fully pressurized, crossover valve 38opens so that some of the oxygen already produced and remaining in sievebed 31 is directed via valve 33 to sieve bed 34. This oxygen helps tostrip or purge nitrogen and other impurities previously filtered bysieve bed 34 during the prior cycle. It is therefore much easier forthese impurities to be evacuated to vacuum reservoir 30. An analogousoperation occurs toward the end of the pressurization cycle of sieve bed34. Oxygen is directed through open crossover valve 38 from bed 34 tobed 31 to assist purging of nitrogen and other impurities from thelatter bed and thereby enrich the oxygen in that bed.

By directing enriched oxygen through the crossover valve before the mainvalve reverses the air flow to the beds, system 10 achieves a number ofbenefits. Prolonged and increased purging is performed in each filter sothat improved nitrogen filtration and oxygen enrichment areaccomplished. Additionally, pressure is relieved/reduced in the bedbeing pressurized prior to, rather than following the end of eachpressure cycle. This reduces the power used by the compressor so thatoperating efficiency and battery life are improved. Concentrator 10therefore represents a significant improvement over less than optimallyefficient conventional systems wherein the crossover valve does operateto purge nitrogen and the pressure in the beds is not equalized untilafter the valves reverse the pressure cycle.

In the foregoing manner, enriched oxygen is continuously produced bysieve beds 31 and 34 in a cyclical, alternating sequence. The oxygen isdelivered to tank 50 and received by patient 54 through flow meter 52 asneeded. Impurities are evacuated from the beds in a reverse alternatingsequence and the check valves restrict reverse flow of oxygen from tank50. The vacuum and pressure reservoirs significantly reduce the pressureexerted on the beds and the compressor while maintaining a high volumeair flow. Efficiency is improved and power requirements are reduced.These benefits are enhanced by utilizing sensors to deactivate the motorwhen the oxygen tank is full, as previously described.

The valves are programmed or otherwise controlled to provide equal airflow volume during each cycle. This optimizes the level of oxygenprovided to the patient. Unlike concentrator sieve beds of the priorart, both beds work at an equal level and produce an equally pure oxygenoutput. This improves the level of enriched oxygen delivered to tank 50.The system of this invention thus operates much more efficiently thanconventional concentrators.

Concentrator 10 uniquely employs pressure and vacuum reservoirs 26 and30, which provide for significant advantages over the prior art. Thesebenefits are as follows.

1. The aluminum or other metal construction of pressure reservoir 26causes the reservoir to act as a heat sink. The reservoir effectivelydissipates heat from the pressurized air produced by compressor 12. Thiscools the air eventually delivered to sieve beds 31 and 34. As a result,the sieve beds operate more efficiently and effectively to produceenriched oxygen.

2. Pressure reservoir 26 significantly reduces the volume of waterdroplets entering the sieve beds. Instead, such water is retained in thepressure reservoir. The water droplets are converted to vapor duringperiods of low pressure so that the beds operate more effectively andefficiently.

3. The use of pressure reservoir 26 significantly reduces the pressureof the air delivered to the sieve beds. As a result, the concentratorrequires less power and the beds filter the air much more efficiently.In fact, when the amperage of the motor is controlled as described morefully below, this allows a greater volume of air to be generated so thatimproved oxygen enrichment is achieved. By the same token, when lesspressure is generated, the motor is far less apt to stall. Because themotor and compressor do not have to work as hard to build high pressure,much less power is required and battery life is significantly prolonged.Extended battery life is especially important for portableconcentrators. The expense and inconvenience at having to continuouschange batteries is significantly alleviated.

4. The presence of pressurized air in reservoir 26 enables a largevolume of air to be introduced into a sieve bed during each cycle whenvalve 28 opens reservoir 26 to that sieve bed. A large volume ofpressurized air is ready to be immediately introduced into the sieve bedso that the production of enriched oxygen is increased significantly.Indeed, a much more effective enriched oxygen production is achievedthan is accomplished by simply pumping air from the compressor directlyinto the sieve bed. Such improved performance also allows much smallerand more easily transportable sieve beds to be utilized. Much lessfilter medium is needed to produce a desired volume of enriched oxygen.

5. Because crossover valve 38 opens just before the end of eachpressurization cycle, the pressure in the concentrator is reduced. Onceagain, the motor and compressor are required to work less. Systemefficiency is improved and battery life is extended.

6. The innovative use of the vacuum reservoir especially improves theefficiency and effectiveness of the concentrator. When valve 28 switchesthe pressure and vacuum reservoir connections to the respective sievebeds, the presence of vacuum reservoir 30 enables the previouslypressurized sieve bed (which is now communicably joined to the vacuumreservoir) to evacuate extremely efficiently and effectively. A highflow of air almost immediately strips nitrogen molecules from the filtermedium in the previously pressurized sieve bed. Impurities are thenremoved through vacuum reservoir 28 to vacuum head 16 and exhaust port24 of compressor 12. A much more effective evacuation of impurities isthereby accomplished than would be achieved without the vacuumreservoir. In addition, vacuum reservoir 30 helps to reduce the totalvacuum drawn by compressor 12. This greatly reduces the overall powerconsumption and further contributes to prolonged compressor and batterylife.

By controlling the amperage of motor 18 rather than the speed (RPM) ofthe motor as is done in the prior art, significant benefits areachieved. In particular, amperage control 20 provides for an efficientand constant power consumption that further contributes to prolongedbattery life. Moreover, the amperage control also accomplishes greaterair flow and therefore improved production of enriched oxygen on initialstart up.

There is shown in FIG. 2 a graph that compares the air volume anddirectly proportional motor speed (RPM) to the pressure generated by thecompressor. In conventional concentrators, the speed of the motor isselected (for example, a representative speed of 2,000 RPM, line 100)and the pressure generated by the compressor gradually builds so that avolume of air 102 is generated.

The concentrator of this invention alternatively utilizes an amperagecontrol circuit 20 that maintains the motor at a predetermined powerconsumption suited to operate effectively with the pressure and vacuumreservoirs 26 and 30. Initially, as represented by line 104, and beforethe air is pressurized, the motor operates at a relatively high speed(e.g. 4,000 RPM) and produces a commensurately high degree of air flow.Gradually, as indicated by arrow 104, the pressure increases while themotor speed and air flow decrease. Nonetheless, this is preferable toconstant RPM control, dashed arrow 100, wherein the air flow or volumeremains the same or decreases slightly as the pressure in theconcentrator builds. Indeed, over the period required to achieve maximumdesired pressure, the amperage controlled concentrator will generate asignificantly greater amount of air flow, as represented by triangularhatched area 106. An increased production of enriched oxygen is therebyachieved. This high flow achieves a significantly improved production ofenriched oxygen in the sieve beds.

Using the amperage control of this system is especially effective whenthe concentrator is employed in high altitude locations. In such cases,the motor speed must typically be higher during initial operation of theconcentrator in order to overcome the lower density of the high altitudeair. Thereafter, the amperage control circuit 20 allows the motor speed(RPM) to constantly change in order to maintain the desired volume ofair flow in the concentrator. An RPM controlled motor is less thansatisfactory in such applications because the air flow remains constant.Amperage control, wherein RPM is gradually reduced after start-up of theconcentrator, is much preferred and provides for a more efficientoperation and improved production of enriched oxygen.

From the foregoing it may be seen that the apparatus of this inventionprovides for an oxygen concentrator that produces enriched oxygen formedical purposes utilizing vacuum-pressure swing absorption. While thisdetailed description has set forth particularly preferred embodiments ofthe apparatus of this invention, numerous modifications and variationsof the structure of this invention, all within the scope of theinvention, will readily occur to those skilled in the art. Accordingly,it is understood that this description is illustrative only of theprinciples of the invention and is not limitative thereof.

Although specific features of the invention are shown in some of thedrawings and not others, this is for convenience only, as each featuremay be combined with any and all of the other features in accordancewith this invention. Other embodiments will occur to those skilled inthe art and are within the following claims:

1. A vacuum-pressure swing absorption oxygen concentrator comprising: anelectric motor; a compressor operated by said motor; a pressurereservoir having an inlet communicably connected to said compressor anda vacuum reservoir having an outlet communicably connected to saidcompressor such that operation of said compressor delivers pressurizedair to said pressure reservoir and draws a vacuum on said vacuumreservoir; a pair of nitrogen filters; and a control valve forsequentially and alternately interconnecting an outlet of said pressurereservoir to communicate with a selected one of said nitrogen filterswhile simultaneously connecting an inlet of said vacuum reservoir tocommunicate with the other said nitrogen filter; whereby pressurized airfrom said pressure reservoir is delivered sequentially and alternatelyto respective one of said nitrogen filters for filtering therein whilepreviously filtered impurities are simultaneously discharged from theother said filter through said vacuum reservoir.
 2. The apparatus ofclaim 1 further including a motor controller for controlling operationof said motor a constant predetermined amperage.
 3. The apparatus ofclaim 1 further including a control mechanism for directing said controlvalve to alternately and sequentially interconnect each of said nitrogenfilters to said pressure and vacuum reservoirs respectively.
 4. Theapparatus of claim 1 further including a crossover valve interconnectedbetween said nitrogen filters, which crossover valve opens prior to arespective one of said filters being fully pressurized by air from saidpressure reservoir such that pressurized enriched oxygen is deliveredthrough said crossover valve to said other nitrogen filter to assist inpurging said other filter of previously filtered impurities containedtherein.
 5. The apparatus of claim 4 further including a controller fordetermining a selected pressure level at which said crossover valveopens.
 6. The apparatus of claim 1 further including a product tankcommunicably connected to an outlet of each said filter for receivingfiltered air therefrom.
 7. The apparatus of claim 6 in which a checkvalve is disposed between each said filter and said tank to direct theflow of filtered air in one direction from said filters to the tankwhile restricting the flow of enriched oxygen from said tank to saidfilters.
 8. The apparatus of claim 1 further including a sensor fordetecting that pressurized air in said tank has reached a predeterminedlevel.
 9. The apparatus of claim 8 in which said motor is programmed tostop operation of said compressor in response to said sensor detectingsaid predetermined level of air in said tank.
 10. A vacuum-pressureswing absorption oxygen concentrator comprising: an electric motor, acompressor operated by said motor; a motor controller for controllingoperation of said motor a constant predetermined amperage; one or morenitrogen filters in selective communication with the compressor; apressure reservoir having an inlet communicably connected to saidcompressor; and a vacuum reservoir having an outlet communicablyconnected to said compressor such that operation of said compressordelivers pressurized air to said pressure reservoir and draws a vacuumon said vacuum reservoir.
 11. The vacuum-pressure swing absorptionoxygen concentrator of claim 10, further comprising a control valve forsequentially and alternately interconnecting an outlet of said pressurereservoir to communicate with a selected one of said nitrogen filterswhile simultaneously connecting an inlet of said vacuum reservoir tocommunicate with the other said nitrogen filter; whereby pressurized airfrom said pressure reservoir is delivered sequentially and alternatelyto respective one of said nitrogen filters for filtering therein whilepreviously filtered impurities are simultaneously discharged from theother said filter through said vacuum reservoir.
 12. A vacuum-pressureswing absorption oxygen concentrator comprising: an electric motor, acompressor operated by said motor; a pressure reservoir having an inletcommunicably connected to said compressor and a vacuum reservoir havingan outlet communicably connected to said compressor such that operationof said compressor delivers pressurized air to said pressure reservoirand draws a vacuum on said vacuum reservoir; a plurality of nitrogenfilters; and a control valve for selectively connecting an outlet ofsaid pressure reservoir to a first one of the plurality of nitrogenfilters while simultaneously connecting an inlet of said vacuumreservoir to a second one of the plurality of nitrogen filters.
 13. Theapparatus of claim 12 further including a motor controller forcontrolling operation of said motor a constant predetermined amperage.14. The apparatus of claim 12 further including a crossover valveinterconnected between said nitrogen filters, which crossover valveopens prior to a respective one of said filters being fully pressurizedby air from said pressure reservoir such that pressurized enrichedoxygen is delivered through said crossover valve to said other nitrogenfilter to assist in purging said other filter of previously filteredimpurities contained therein.
 15. The apparatus of claim 14 furtherincluding a controller for determining a selected pressure level atwhich said crossover valve opens.
 16. The apparatus of claim 12 furtherincluding a product tank communicably connected to an outlet of eachsaid filter for receiving filtered air therefrom.
 17. The apparatus ofclaim 16 in which a check valve is disposed between each said filter andsaid tank to direct the flow of filtered air in one direction from saidfilters to the tank while restricting the flow of enriched oxygen fromsaid tank to said filters.
 18. The apparatus of claim 17 furtherincluding a sensor for detecting that pressurized air in said tank hasreached a predetermined level.
 19. The apparatus of claim 18 in whichsaid motor is programmed to stop operation of said compressor inresponse to said sensor detecting said predetermined level of air insaid tank.